The development of a simple and effective continuous light dual and multiwavelength spectrophotometer which may be worn during strenuous exercise or applied to the head of the smallest pre-term neonate affords a challenging design and evaluation program which is to be met by the combination of improved electro-optic transducers and microminiaturization techniques. Such units are expected to command a wide market for "rend monitoring" of hemoglobin and myoglobin deoxygenation in health and disease. Calibration of the pathlength of such instruments is afforded by the novel technique of time-resolved spectroscopy (TRS) which actually measures the distance that the light photons travel from input to output and therefore allows correct calculation of concentrations or concentration changes based upon the Beer-Lambert law. The theoretical background for photon migration in tissues is explained and the theoretical basis for calculation of absorption per unit pathlength (mu cm -1) is provided. The practical application of this technology to human subjects in an affordable phase modulation time resolved spectroscopy system will be feasibility tested. Dual and multiple wavelength Year 1 feasibility test systems and Year 2 production prototype systems are described. It is envisaged that our exclusive multiwavelength phase modulation TRS will replace existing continuous light systems as a front and for the roughly half dozen production models of hemoglobinometers which have been elaborated for critical care by other companies. A large market for the phase modulation TRS system is predicted.